Polysaccharides tetrasaccharides

This group includes a set of anionic polysaccharides secreted by unrelated bacteria. The common theme, however, is that their main chains have the same tetrasaccharide repeat. Although (high acyl) native gellan (42) and (deacylated) gellan (40,41) are linear polymers, welan (43) is a branched polymer in which a monosaccharide side chain is regularly attached to each repeat. Other members of this family, such as S-657 and rhamsan, are also branched, like welan."0... 

The difficulties inherent in obtaining correct sugar analyses for a polysaccharide containing three different amino sugars are obvious. It therefore seems possible that S4 is composed of tetrasaccharide repeating-units, containing one residue each of the four different sugar components. 

GELLAN. The extracellular, anionic, linear polysaccharide from Pseudomonas elodea, is called gellan in its deacylated form. It is industrially important because of its ability to form cation-dependent gels. Its tetrasaccharide repeating motif (A-B-C-D) is given below ... 

The basic extensins. These are hydroxyproline-, lysine- and tyrosine-rich glycoproteins consisting of rigid molecular rods about 80 nm long (14,15), bearing short mono- to tetrasaccharide side-chains (2,14). When newly secreted they bind ionically to the acidic polysaccharides of the cell wall and can be extracted with cold salt solutions later they become much more resistant to salt-extraction and are said to be covalently bound, probably via dimerization of their tyrosine residues to form isodityrosine (15). 

Although the isolation and identification of new disaccharides, tri-saccharides and tetrasaccharides and their derivatives, either by acid hydrolysis or by controlled oxidative degradation, " would be of great help in these studies it would appear to be worth while to develop other indirect methods of approach involving the use of enzymes capable of effecting scission at specific points in the molecular complex. Better methods for the quantitative separation of sugars and their derivatives are in the process of development and it is not unlikely that in the near future it will be possible to derive formulas not only for plant gums but for the many related complex polysaccharides. 

Generally, carbohydrates are classified into four different categories, monosaccharides, di-, tri- and tetrasaccharides, oligosaccharides and polysaccharides. 

When the extracellular, acidic polysaccharide from Rhizobium meliloti IFO 13336 was hydrolyzed with extracellular /3-D-glycanase and then intracellular endo-(l - 6)-/J-D-glucanase, two tetrasaccharides were... 

Another example of O-specific polysaccharides that are assembled through the block mechanism are the polymers from Salmonella serogroups C2 and C3. Their polysaccharide chains (18) are composed97 of linear, tetrasaccharide repeating-units having abequosyl and D-glucosyl branches,... 

Synthesis of the tetrasaccharide repeating-unit of the O-specific polysaccharide from Salmonella senftenberg. Carbohydr. Res. 5 1, 269-27 1... 

Kochetkov, N.K., Torgov, V.I., Malysheva, N.N., Shashkov, A.S., and Klimov, E.M. (1980a). Synthesis of the tetrasaccharide repeating-unit of the O-specific polysaccharide from Salmonella muenster and Salmonella minneapolis. Tetrahedron 36. 1227-1230 Kochetkov, N.K., Torgov, V.I., Malysheva, N.N., and Shashkov, A.S. (1980b). Synthesis of the pentasaccharide repeating-unit of the O-specific polysaccharide from Salmonella Strasbourg. Tetrahedron 36, 1099-1105... 

The details of the synthetic approach we have adopted for the preparation of all possible di- and trisaccharide sequences of the Y polysaccharide repeating unit have been published (16-19), together with the syntheses of two of the four possible tetrasaccharides (19,20). The synthesis of a third tetra-saccharide sequence not previously reported is described below. 

The substrate, i,e. the O-antigenic polysaccharide chain, can carry several substituents on the basic tetrasaccharide repeating unit in form of D-glucose residues or O-acetyl groups (Figure 7). 

Shigella flexneri LPSs comprise a large family of interrelated O-polysaccharide structures, the simplest of which belongs to the Y variant polysaccharide (Table 3). This has a tetrasaccharide repeating unit containing three L-rhamnose residues and... 

Fig. 27 a, b. Tetrasaccharide with two repeating disaccharide units from Klebsiella capsular polysaccharide K23 in its two energetically favored conformations... 

The primary structure of the Klebsiella K8 capsular polysaccharide was established by Sutherland (3). It is a poly(tetrasaccharide) with three sugar residues in the backbone and a monosaccharide side-chain (II). 

Figure 6. The tetrasaccharide repeating unit of Klebsiella K8 polysaccharide showing the atom labeling. The residue A is ft-D-glucose B is a-D-galactose C is /3-D-galactose and D is a-D-glucuronate.

In V. Cholerae, the Galp residue carries a 4,6-cyclic phosphate. The same repeating unit was found in the capsular polysaccharide. Multidimentional he-teronuclear NMR and molecular-modeling studies showed that the 0139 tetrasaccharide adopts a compact and tightly folded conformation that is relatively rigid and similar to the Leb conformation. The cyclic phosphate on the (3-galactopyranoside residue is in contact with the colitose residue linked to (3-GlcNAc.209 The capsular polysaccharide has been proposed as the basis for vaccine development.210... 

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